A T1 transmission line, also referred to as a DS1 line, is a dedicated telephone connection that may support data ranges of up to 1.544 Mbits per second (Mbps). A T1 line may have 24 individual channels, each of which support 64 Kbps. Each 64 Kbps channel may be configured to carry digital data that may represent voice or other types of analog data, or purely digital information.
E1 is the European format for digital transmission and is similar to the North American T1. E1 carries signals at 2.048 Mbps (32 channels at 64 Kbps). E1 and T1 lines may be interconnected for international use.
T1/E1 transceivers may receive and transmit digital signals over a telephone communication transmission line to a connecting communication system, for example, a business computer network. T1 (and E1) lines may be used as a leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone.
Data transmitted over a T1 line may be formatted in frames comprising a predetermined number of bits, e.g., 193 bits for a standard T1 frame 100 including twenty-four time slots 102, as shown in FIG. 1. The frame may include payload information and signaling information. The payload information contains the digital representation of the originally transmitted voice/data signal. Signaling information may represent phone receiver status (e.g., on-hook or off-hook) and other service type information.
A framer at the transmission line/system interface may extract the signaling information from the payload information in the frame. The payload information may be switched by a cross connect over dedicated circuitry according to a switching table. The cross connect may also include dedicated circuitry for switching signaling information separately from the associated payload information. Such additional dedicated circuitry may increase the size and complexity of the cross connect and reduce the operational flexibility of the device.